Not sure on '74-'77s how front or rear bumpers are scored, but let's say the rear bumper is worth 16 points. 8 for originality + 8 for condition. On the fiberglass bumper it most likely would be a full deduct(-16) because it's not made of urethane and it's not a GM part. Kinda like "zero" points for a Fram oil filter or air filter(non GM part). On the other hand, the new non indented GM bumper might receive all points if you used the larger script rear emblem. The judges may/may not catch the "early VIN/small rear emblem" scenario. Even if they might and you were up front with them about what you "had to do" because the small script indented bumper isn't available, it might only be a few point deduction on "originality".